When Los Altos-reared writer Galit Breen penned a Huffington Post blog about the secrets to a happy marriage, she knew better than to expect commenters to say nice things about everything she wrote. After all, this was the Internet.

But she wasn’t prepared for readers to attack her viciously for how she looked in her wedding photos. One reader derided the site for loving fat women, and another called her a “heifer.”

She had become the latest victim of fat-shaming, a particularly noxious but widespread form of cyberbullying.

After going to a “sad place,” the mother of three turned the tables on her cyberbullies. She called them out in a new post for the online women’s magazine XOJane that won her a book deal. “Kindness Wins,” her guide to teaching kids to be nice online, was published in April.

“In my experience, girls’ bodies are assessed and talked about much too often,” writes Breen, a San Jose State graduate and former elementary school teacher who now lives outside Minneapolis. “You’re so thin/fat/hot/not. … Oh my goodness, enough!”

Breen is among a growing number of bloggers, “body positive” activists and celebrities, from Jennifer Lawrence to Amy Schumer, who are likewise saying “enough.”

And many are using the Internet, today’s epicenter for fat-shaming, to speak out against a culture that tells people they should feel lousy if their bodies don’t conform to what experts say are extremely unrealistic beauty ideas.

Through blogs and social media, these women — including Chrystal Bougon, owner of San Jose’s plus-sized lingerie shop Curvy Girl, San Francisco body image expert Virgie Tovar and Brittany Gibbons, author of the new New York Times best-selling book “Fat Girl Walking” — are challenging institutions and businesses that foment negative attitudes toward overweight people. Among the examples:

A 25-year-old plus-sized photographer early this month proudly posted a selfie of herself in an Old Navy dressing room that went viral. It shows Rachel Taylor trying on a body-clinging, American flag tank top that she laments had drawn ridicule from other customers for being available in large sizes. Taylor’s selfie comes half a year after Old Navy responded to a Change.org petition protesting pricing policies for plus-sized clothing.

In June, the popular discussion website Reddit likewise bowed to growing pressure to address abusive online behavior by banning five controversial subreddits, including one called Fat People Hate, which had more than 150,000 subscribers.

Bougon thinks that her Curvy Girl customers, who were disparaged on Reddit’s fat-shaming threads for posing for her store’s Facebook page in sexy lingerie, were among those who successfully protested for the website to update its anti-harassment policy.

Not surprisingly, Victoria’s Secret has been a favorite target of online activism and ended up apologizing for last year’s “Perfect Body” campaign, featuring apparently size-0 models.

“It’s funny, because the Internet is this incredible machine of hatred and shame, but it’s also a vehicle for creating momentum for the movement,” Tovar says. “What’s exciting to me is that social media didn’t create fat activism, it galvanized it. It was only a matter of time before people who were feeling the same way — that our diet culture was awful — would get together and talk to each other.”

Jes Baker, a blogger in Tucson, Arizona, had long felt bad about her size-20-22 body. That changed three years ago, when she discovered blogs where other chubby women posted essays and selfies depicting themselves as confident and admired.

“I remember looking through the pictures and being shocked at first, but that was really an ‘aha’ moment,” she says. “I realized I don’t have to hate myself for the rest of my life. I had no idea that being fat and happy was an option. And once you know something, you can’t un-know something.”

Penning a ‘manifesto’

With her blog, The Militant Baker, Baker gained national attention when she created a public relations headache for Abercrombie & Fitch CEO Mike Jeffries. She called him out for saying that anyone who doesn’t fit an all-American “cool kid” idea of beauty shouldn’t be wearing his clothes. She accompanied an open letter with a mock Abercrombie & Fitch ad, featuring her topless self and a hunky male model.

In October, Baker, who founded the Body Love Conference, will publish her book, “Things No One Will Tell Fat Girls.” She describes it as a “manifesto” for women of all sizes to love themselves and change societal perceptions of what’s attractive, a message she thinks resonates in a time when people are embracing diversity of all kinds.

These self-acceptance messages also come at a time when as many as 30 million people in the United States have an eating disorder, and high levels of body dissatisfaction lead most college-age woman to diet, according to the National Association of Anorexia Nervosa and Associated Disorders.

Weight discrimination also is one of the most prevalent forms of discrimination, notably in the workplace, with women saying it happens on levels comparable to racial discrimination, says Rebecca Puhl, deputy director of the University of Connecticut’s Rudd Center for Food Policy and Obesity.

“Unfortunately, when there are widespread societal perceptions that body weight is a simple matter of personal control, discipline or willpower, it becomes very easy to attribute blame, shame and negative stereotypes toward people who have a larger body size,” she says.

Many activists say today’s worship of the impossibly thin body has intensified in our digital era. Not only do images of supposedly perfectly proportioned women bombard us through TV and mobile screens, photo-editing technology makes it easy to trim models’ waistlines, hips or thighs before publication.

Activists also raise concerns that well-meaning public health campaigns to fight obesity have provided body-shaming ammunition to everyone from online trolls, saying confident overweight people set a bad health example, to health and fitness entrepreneurs using fear about heart disease and diabetes to sell diets or exercise programs that can lead to destructive cycles of yo-yo dieting.

“I understand the intentions, but kids coming into our program are bombarded with information in ways they can’t comprehend,” says Lisa Peterson, the clinical director at the Eating Recovery Center of California in Sacramento.

‘Regular Women’

The pressure for people to diet and lose weight to be deemed “healthy” hit Curvy Girls’ Bougon and her customers hard after she launched her “Regular Women” Facebook campaign in 2013.

Posting snapshots of large women in sexy lingerie won her thousands of new Facebook friends. But it also enraged anonymous commenters on Reddit and other sites and put her in the cross-hairs of Maria Kang, a Sacramento fitness expert and blogger known as “Fit Mom.” Bougon and Kang debated the issue on CNN, with Bougon telling Kang that her scolding people for weighing too much won’t motivate them to diet or exercise.

“You might be fat today, you might not be fat tomorrow, but whatever you look like today, you get to look and feel as beautiful and as sexy as possible,” Bougon said.

For Bougon, the attention was initially bruising, but it boosted sales. It’s no surprise that she’s a fan of the idea that a good way to reduce fat stigma is to convince companies it’s good business to use actual-sized models in their marketing campaigns.

Indeed, a University of Kent study last year in England asserted that average-sized models could actually sell more clothes for retailers than their size-zero counterparts.

Pop culture’s embrace

Some companies have already moved in that direction. While not a clothing company, Dove several years ago began using non-models to market skin care products with its Real Beauty campaign. Earlier this year, San Francisco-based online retailer Modcloth enlisted employees of all shapes and sizes to star in the site’s new swimsuit ads.

In pop culture terms, large-sized women have been enjoying the spotlight lately. Plus-sized supermodel Tess Holliday graced the cover of People magazine, Melissa McCarthy killed at the box office with her action-comedy “Spy,” and critics have praised the male stripper romp “Magic Mike XXL” for depicting women of all sizes enjoying their sexuality.

To promote “Trainwreck,” her comedy coming out this weekend, ﻿comedian Schumer proclaimed: “I have a belly. And I have cellulite. And I still deserve love.”

To activists, such statements offers hope that society, however slowly, is opening up to diverse ideas of beauty. Speaking of efforts by writers such as Breen, Gibbons and Baker, Tovar notes that not so long ago, publishers would have turned up their noses at their messages of fat acceptance. But those women built their own online buzz, and the body positive movement is, in some ways, coming into style.

“Now publishers are scrambling to get them,” she says.

‘Body Positivity’ Resources

Galit Breen’s “Kindness Wins” (Booktrope Editions, $11.95) is a guide to teaching kids to be kind online, and it includes Breen’s personal story of fat-shaming to illustrate why it’s no longer OK “to talk about other people’s bodies — ever.” She also blogs at www.theselittlewaves.com.

Brittany Gibbons is author of the new New York Times best-selling “Fat Girl Walking: Sex, Food, Love, and Being Comfortable in Your Skin … Every Inch of It (Dey Street Books, $24). In her memoir, the mother of three writes humorously about overcoming her body self-hatred, about her decision to post photos of herself in a bikini and how she’s become a happy, fashion-forward champion of women. She also blogs at www.brittanyherself.com.

Jes Baker’s blog, The Militant Baker (www.themilitantbaker.com), features her sassy, no-holds-barred photo-illustrated posts with titles such as “I wear what I want.” She also opens up about insecurities and challenges media figures, corporations and attitudes that encourage prejudice against overweight people. Her book, “Things No One Will Tell Fat Girls” will be published by Seal Press in October.

Martha Ross is a features writer who covers everything and anything related to popular culture, society, health, women’s issues and families. A native of the East Bay and a graduate of Northwestern University and Mills College, she’s also a former hard-news and investigative reporter, covering crime and local politics.